This gets to one of my pet peeves. The conversation usually goes like this..

/me "I'll take a medium soda."
/them "we don't have mediums. Just small, large, and extra large"
/me "wouldn't your large be a medium then?"
/them "I guess"
/me "okay, I'll take a medium soda"
/them "would you like to biggie/super/king size that for an additional $.39?
/me "cancel my drink, I'll get something at home."

and as for the sub debate, my vote goes to cousin's.